Abstract
A novel one-trough synthesis via an air-water interface is demonstrated to provide hexagonally packed arrays of densely spaced metallic nanoparticles (NPs). In the synthesis, a mesostructured polyoxometalate (POM)-silicatropic template (PSS) is first self-assembled at the air-water interface; upon UV irradiation, anion exchange cycles enable the free-floating PSS film to continuously uptake gold precursors from the solution subphase for diffusion-controlled and POM-site-directed photoreduction inside the silica channels. NPs ≈ 2 nm can hence be homogeneously formed inside the silica-surfactant channels until saturation. As revealed via X-ray diffraction, small-angle X-ray scattering (SAXS), grazing incidence SAXS, and transmission electron microscopy, the Au NPs directed by the PSS template are arrayed into a 2D hexagonal lattice with inter-channel spacing of 3.2 nm and a mean along-channel NP spacing of 2.8 nm. This corresponds to an ultra-high number density (≈1019 NPs cm-3) of narrowly spaced Au NPs in the Au-NP@PSS composite, leading to 3D densely deployed hot-spots along and across the mesostructured POM-silica channels for surface-enhanced Raman scattering (SERS). Consequently, the Au-NP@PSS composite exhibits prominent SERS with 4-mercaptobenzoic acid (4-MBA) adsorbed onto Au NPs. The best 4-MBA detection limit is 5 nm, with corresponding SERS enhancement factors above 108. Densely arrayed metallic nanoparticles are fabricated via self-assembly of a mesostructured polyoxometalate-silicate-surfactant (PSS) template at the air-water interface (left), followed by adsorption of metallic precursors to the PSS film via anion exchange (middle), then finished by polyoxometalate (POM)-site-directed photoreduction of the metallic anions and formation of metallic NPs inside the silicate-surfactant channels upon UV irradiation (right).
Original language | English |
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Pages (from-to) | 2544-2552 |
Number of pages | 9 |
Journal | Advanced Functional Materials |
Volume | 24 |
Issue number | 17 |
DOIs | |
Publication status | Published - May 2 2014 |
Externally published | Yes |
Keywords
- GISAXS
- SERS
- arrayed nanoparticles
- hot spots
- mesostructures
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- General Chemistry
- Condensed Matter Physics
- General Materials Science
- Electrochemistry
- Biomaterials